Paleontologist Neil Shubin holds part of a fossil from Tiktaalik roseae. Dan Dry

What was the first life on earth?

What was the first lifeform like? What was the first fish or mammal? Is it even possible to know? In this episode, we look to the fossil record to help us trace our roots back to the Last Universal Common Ancestor. Paleontologist Neil Shubin joins us to talk about discovering a remarkably cool fossil that helped us understand how life evolved over billions of years. We also take a field trip to the Hall of Ancestors and examine a few branches on the tree of life. And we learn why figuring out how life began on earth could help us as we find life elsewhere in the universe.

What was the first life on the planet?

Many listeners have written in with questions on a similar theme: How did the first organism develop? What was the first life form like? What was the first life on this planet?

These aren’t easy questions to answer but they’re questions that scientists are also really interested in.

The very first organisms most likely didn’t leave fossils behind so in order to figure out how these early, living things came to be, scientists are trying to recreate life from scratch. They’re using only the basic ingredients thought to be on Earth 3.8 billion years ago, when life began.

“We try to put together the most probable scenario using experiments and theory,” said Kate Adamala, a scientist from the University of Minnesota. “We’re trying to put together a scenario of the origin of life that fits with all our known knowledge and that’s reproducible.”

Here’s what scientists think the early days of the planet were like: The Earth formed around 4.6 billion years ago. It was really hot and it was also sterile, meaning there was nothing living on it, but there were lots of different small molecules.

Once the Earth began to cool down, liquid water started to collect on the planet’s surface. This eventually became oceans.

Molecules were floating around in this water, and it happens that water is where chemical reactions like to happen. Scientists think these molecules eventually came together to form things like enzymes and proteins and these eventually came together inside membranes to form primitive cells.

Kate makes very tiny soap bubbles in her lab to try to model what those early cells may have been like (it turns out cell membranes today are actually chemically similar to soap bubbles).

Researchers theorize that eventually these primitive cells laid the groundwork for the first single-celled organism that could be considered alive, meaning it was able to both fuel and make copies of itself. In all likelihood, there was more than just one, single, first, magic living cell.

“There were probably several populations of slightly different cells that became one way or another alive. And only one of them made it further,” said Kate. “That’s why all known lifeforms on earth are descendants of one population. One was the winner but that doesn’t mean they were the only one competing.”

This makes some scientists wonder, what if another kind of cell was successful too? What if there was a type of life that was nothing like the life we know?

“There’s actually this idea that people call shadow biosphere, that it’s not impossible that there is some other independent origin that still survived until today on Earth,” Kate said. “If we find another form of life how we would know that it’s from a separate origin and how would we define life? How would we know it’s alive?”

This kind of work not only helps us figure out how life started on this planet, it will also help scientists as they look for life elsewhere in the universe.

Think about it: What if we land on Jupiter’s moon Europa or send a rover to another planet and when we get there we don’t see any creatures moving around? That doesn’t mean the planet is lifeless. What if something that looks like rust to us, is actually a living organism? If we really want to find alien life, we need to be able to imagine lifeforms that look nothing like what we’ve seen here on Earth.

“If it is originated in a different place it won’t be a green little man, it might be some kind of slime,” Kate said. “How do you know it’s alive?”

More on Tiktaalik
A model of a newly discovered species, Tiktaalik roseae, that fills in the evolutionary gap between fish and land animals, depicted in what scientists believe to be the animal's environment about 375 million years ago. Model by Tyler Keillor, Photo by Beth Rooney | University of Chicago

More fossil photos
A computer model and virtual development of the tooth plate of Romundina stellina, with colors gold through purple indicating the first up to the final tooth addition. Martin Rücklin | Naturalis Biodiversity CenterStromatolites at the Los Angeles County Natural History Museum. Sanden Totten